Treatment of boiler feed water



Patented Mar. 11, 1941 UNITED s'rares TREATMENT OF BOILER FEED WATER,

Ernest F. Walsh, Warwick, R. 1., minor to The Narraransett ElectricCompany, a corporation '01 Rhode Island No Drawing.

13 Claims.

This application is a continuation in part my co-pending application,Serial No. 160,889, filed August 25, 1937. This invention relates to thetreatment of waters used in steam boilers, and in particular. to naturalwaters carrying scale-forming ingredients for use in steam boilers iorsteam-generating purposes at high boiler pressures; and has for one ofits objects the external treatment of the raw boiler feed water in sucha manner as to completely remove there from, before it is introducedinto the boiler, those ingredients which tend to form a hard adherentBil All

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scale within the boiler at the high operating temperatures'and pressuresof the latter.

Another object of the invention is to provide clean, dry steam which isfree trom solids and oi" n duality/that the efilciency and capacity ofthe prime movers are maintained.

Another object of the invention is the external treatment oi the boilerfeed water in such a manner that all undesirable adherent scaleiorminesalts, particularly calcium, magnesium and silica, which causepermanent. hardness in the reed water are completely removedprior to itsintroduction in the boiler, and thereby prevent the iormation oisulphates and hydroxides of such salts in the water within the steamboiler.

Another object of the invention is to provide a one-step method ofconditioning the raw boiler feed water so as to completely remove fromsuch vvater before it enters the boiler all the scaletormirig materialswhereby the treated water may .be used directly for boiler iced purposeswithout subsequent or secondary chemical treatment in the boiler.Another object or the invention is the provision oi. a method oitreatinr boiler iced water with a phosphate materiel irrespective or thepltl value oi the raw Water used so as to obtain substantially completereaction oi the phosphate with the scale-forming solids in the rawwater.

Another object of the invention is to provide a method of conditioninenatural waters used tor boiler feed purposes bytreatrnent outside oi theboiler in which the removal of the scale i'orrnine elements and thesoftening and dcaeration of the boiler feed water is effected in asinrle treating apparatus.

in the continuous operation oi steam boilers of lures industrial orcentral power plants for steam generation at high temperatures andpressures, especially those utilizingpressures in excess of rose poundsper square inch gauge, it is essential if optimum conditions are toprevail that there be always available for boiler feed purposes aplentiful supply of water which is free of scaleiorniing ingredients inorder that the formation oi hard adherent scale within the boiler beavoided and to obviate corrosion, priming, or other undesirable efiectswithin the steam boiler.

Application Serial No. 344,07

July 5, 1940, 5

operation of such power plants is to employ some chemical method oftreatment for conditioning the water used to render it suitable forboiler purposes.

Various forms of chemical treating materials and their application haveheretofore been proposed or are in use which, under controlledconditions, produce a non-adhering scale or sludge, thereby preventingthe formation of such destructive scales or incrustations, as calciumsulphate, calcium silicate, magnesium silicate, calcium hydroxide andmagnesium hydroxide. The standard methods of relie! ordinarily employedfor the treatment or the raw ieed water to over come the effects of suchundesirable ingredients fall into two eroups: (it By internalconditionins oi the water within the boiler by means oi chemicalsubstances, and (2) by the chemical treatment of the boiler feed wateroutside of the boiler before introducing it into the boiler followed byinternal treatment.

in commercial power plant operation, the general practice is to utilizethe second of the abovenamed methods of treatment of the water'used inthe boiler, the first step oi which comprises a primary treatment oi theraw feed water to soften it before introducing it into the boiler, as bymeans of either the regular lime-soda process, or by a base eirehangeprocess, such as the zeolite process, for removing the major portion oithe scale-iormine ingredient from the raw iced water, Alter beingsubjected to this primary treatment, the feed water is then elven asupple mentally or secondary chemical treatment after being introducedinto the boiler so as to maintain either a carbonate or a phosphate ioneon eentration in the boiler Water to prevent the formation oi adherentscale by any scaledcmrlng ineredients not completely removed from theiced water by the preceding primary treatment.

The lime-soda process is commonly used as the primary external method oitreatment of the raw boiler reed vvater Where the natural water containscalcium and magnesium salts, causiue them to be precipitated in the formof insoluble carbonates in the softener or treating apparatus,

The secondary follow-up treatment or the boiler feed water requiring theaddition or chem icals to condition the water in the steam boiler,causes the insoluble, non-adherent sludges to form within the steamboiler. The resulting precipitates in such cases cause deposits whichcollect on the surfaces of the metal or remain in suspension in thecirculating Water, thereby requiring frequent blowing down of the boilerwater to prevent building up of excessive con-'- centrations within theboiler. Sludge accumu til) lations cause the interruption of propercirculation in parts of the boiler, and the steam produced containssolids which are troublesome and are carried over to adhere to theblading of the turbines and the interior surfaces of other prime movers,thereby resulting in a considerable reduction in their output capacityand impairment of their efficiency.

Of the various standard methods of internal conditioning of the water inthe steam boiler, the two principal methods ordinarily used incommercial power plant practice for this secondary treatment arechemical methods of treatment which employ either a carbonate or aphosphate of an alkali metal added to the water in the steam boiler forthe prevention of formation of the detrimental adherent scale in theboiler. In the practice of these prior internal conditioning processes,the method generally used for boilers operating at low pressures,namely, those under two hundred pounds per square inch gauge, is thesodium carbonate treatment of the water within the boiler, owing to theconvenience and cheapness of this treating material, and one convenientmanner in which such a method may be carried out is described in thePatent to Hall, No. 1,613,701 of January 11, 1927.

For high boiler pressures, viz., those above two hundred pounds, it isthe practice to add to the water in the boiler a phosphate in place ofthe carbonate radical, since the former substance is found to decomposeless readily as the carbonate at the higher operating pressures. Thisdecomposition of the carbonate increases the hydroxyl radicalconcentration of the boiler water, which acts to cause dissolution ofthe metal of the boiler and tends to bring about "caustic embrittlementwithin the boiler. This prior phosphate treatment involving the internalconditioning of the water in the boiler and employed as a secondarymethod of treatment of eflluent water from a lime-soda softener is morefully described in the Hall Patents No. 3,656, of January 11, 1927 and1,903,041 of March 28, 1933.

In these patented methods, however, in order that the reactions of theinternal treatment may be best accomplished, the pH value of the watermust be about 11.0 or 11.5 which with reference to my method isrelatively high and to be avoided. However, in carrying out the priorinternal treatment of the water in the boiler with the use of phosphatesfor the prevention of the formation of adherent scale-forming salts, Ihave found that while the method works satisfactorily at moderatepressures from the standpoint of scale prevention, it is objectionablesince its use causes the formation of a precipitate in the boilersconsisting primarily of calcium and magnesium phosphates, and excessivecarry-over by the steam of these solids which are deposited upon theblading of the prime movers. This type of operation requires frequentcleaning of the equipment to maintain efiiciencies and frequent blowingdown of a considerable percentage of the boiler water to keep the solidspresent in the water at a minimum.

Under the present practice ofhigh pressure boiler operation forsteam-generation, the concentration of solids in the boiler water cannotbe kept to the where steam of desirable quality can be obtained withoutsacrificing efliciency.

In order to overcome the disadvantages of the prior art methods abovedescribed, I have found it to be of advantage to utilize a one-stepexternal method of treatment of the boiler feed water containing thedetrimental scale-forming ingredients, before introducing it into theboilers and which will completely remove from the water all of theobjectionable scale-forming salts, particularly, calcium, magnesium andsilica, and with no subsequent or secondary follow-up treatment of thewater in the boiler being employed, as has heretofore been a requiredstep in the practice of prior art processes; and in the improved methodwhich constitutes the present invention I have found that the practiceof the same will accomplish all that is possible with the previoustwo-step methods of treatment involving the combined external andinternal conditioning methods, but with the additional resuit that asuperior quality of steam of low moisture and solid content is producedin the boiler which is not possible to secure from the completelytreated water by the previous internal methods utilized after theprimary softening treatment; the resultant steam of this latter processcontaining excessive moisture and solids of a quality whichdetrimentally affects the efilciency and capacity of the prime movers ofthe system. To this end, I have provided a method of water treatment inwhich a phosphate of an alkali metal is used, and added to the raw feedwater external to the boiler, in conjunction with a catalyst, to causecomplete removal of the cal cium, magnesium and silica in the feedwater. In addition, most of the oxygen and other dissolved gases arealso removed from the feed water, after which the water thus treated ispassed through suitable filters following the treating tank to removefrom the treated water. before its introduction into the boiler, anysuspended solids resulting from the chemical reaction in the treatingtank and of a size which is too fine to be easily separated by their ownweight from the treated water.

In carrying out my novel process I find that I may use a phosphate of analkaline metal to react with the calcium, magnesiumand silica in the rawwater external to the boiler, and while this phosphate formerly did notcause a complete conversion of the mineral solids unless there waspresent heat and a relatively pH value, such as 11.0 or 11.5, I amenabled by the use of a catalyst such as for instance, an iron ion, toobtain a complete reaction of the phosphate with the calcium andmagnesium with lesser heat and in water having a lower pH value. It isdesirable that the boiler feed water have a lower pH value in order thatthere will be less carrying-over of solids by the steam into the bladingof the prime movers of the system.

In carrying out this process the hydrogen iron concentration or pH valueof the water under treatment determines the particular form of phosphateto be used. At present in the carrying out of my invention I prefer toemploy disodium phosphate having a chemical formula of NaaI-IPO4.H2O asa source of the phosphate radical, but I may also use other well-knownforms of sodium phosphate such as sodium tribasic phosphate Na3PO4.H2Oor sodium monobasic phosphate NaH2PO4.H2O with equally satisfactoryresults, the form selected depending upon the pH value of the raw waterto be treated and the pH value of the catalyst to be added.-

In practice of the present invention, a slight' excess over thetheoretical amount of an alkali iron ion, acting as a catalyst, speedsup the chemical reaction of the phosphate with the calcium and magnesiumsalts, since without the presence of any catalyst the action is found tobe slowed down appreciably, preventing the complete re-- action betweenthe calcium and magnesium salts and the phosphate, The reactioncontinues as the treated water passes through the feed pumps, heatersand feed lines from the deaerator to the steam boiler causingtroublesome deposits, However, when the phosphate is used in.conjunction with the small amount of catalyst in accordance with thepresent in-' vention, the phosphate reaction is completed rapidly in thetime during which the water undergoing treatment is in the deaeratortreating apparatus, which usually occupies a period of about an hour, sothat all of the calciumand magnesium salts are precipitated out of theraw water and there is no further chemical reaction with any suchscale-forming substances along the path of the feed water as it is fedto the boiler.

In one form of my invention, as at present practiced, I- prefer toemploy my process in connection with the treatment of rawwater-containing scale-forming solids, the treated water being used inthe boilers of a steam-generating plant of the jet condensing type, inwhich the make-up water fed to the steam boilers to compensate for theloss of steam, amounts to an average of drawn from the city mains. As anillustrative example, the analysis of one typical specimen of rawmake-up water used, showed:

Parts per million Carbonate (CO3) alkalinity as CaCOa 11.6

Bicarbonate (H003) alkalinity as CaCOa 4.7

Total 16.3

Calcium hardness alkalinity as CaCOa 22.28 Magnesium hardness alkalinityas CaCOs 4.94 Carbonate hardness alkalinity as CaCO3 16.30 Non-Carbonatehardness alkalinity as CaCOa 15.74

Total hardness 32.04

As a specific example of my invention, I pass the raw water through afeed water heater of appropriate construction, as is well known in theart, in which the temporary hardness in the raw water is removed byboiling, which operation usually requires a period of from thirtyminutes to an hour, in order to obtain precipitation of the calcium andmagnesium carbonates and bicarbonates to the limit of solubility. Forsuch purposes, however, I prefer to use the Cochrane type of apparatus,which construction combines the deaerator with a feed water heater.During the course of the operation of this form of heater, 9.

temperature of approximately 230 F. is maintained inside the apparatusin which the water being treated is heated by direct contact withextracted steam at about eight pounds gauge pressure. It is alsodesirable that this apparatus have a. capacity equivalent to the maximumhourly demand of the boilers, and also be 0! such a construction thatthe precipitated products of reaction may be easily drawn off while theequipment is in service.

As deaeratio'n of the water in the feed water heater apparatus goes onto remove oxygen and other gases therein, the treating chemicalscomprising the phosphate and the catalyst for removing ingredients whichimpart permanent hardness to the raw water, viz., the calcium, magnesiumand silica salts; are added. For practical reasons, it is desirable thatthe phosphate and catalyst used for treatment of the boiler feed watershall be added so as to bear a definite relation to the rate of flow ofthe water to the deaerating apparatus or treating tank.

In practice, this is attained by the use of a 50-.

called mechanical proportioning device which preferably shall be of aconstruction capable of adjustment for providing a variety of diiferentrates of injection of the treating chemicals. This device preferably isadjusted to feed the iron catalyst which is in the form of an iron ionin solution and obtained from the ferric hydroxide, the ferric chlorideor ferric sulphate in a ferric hydroxide form as above stated, into thefeed water undergoing treatment at the same time as the phosphate and atthe rate of approximately two parts of the iron ion to one million partsof water, and with sufflcient phosphate of the proper form for the pH ofthe water to be treated and slightly in excess of the volume theoreticalrequirement to maintain in the eflluent leaving the deaerating softenerapparatus a phosphate concentration of from one-half to five parts permillion so that the resultant completely treated water will have zerohardnew. At the conclusion of this process, the treated water is foundto have from to 99% of the calcium and magnesium salts precipitated outwhile suitable filters remove the rest of the suspended solids.

Any sulphates, oxides of iron and alumina contained therein as solublesalts will, however, go through into the boiler without beingprecipitated or removed from solution in the feed water.

In order that the phosphate and the catalyst materials, which in theircommercial form usual- 1y are in powdered condition, may lieincorporated in the water to be treated so that a uniform mixture willresult, I preferably add these materials to thewater in the treatingtank in the form of a previously prepared solution, which is fed to thetreating tank at the desired rate of feed by the so-called mechanicalproportioning" device. As a specific example of such a treating solutionwhich may be used for treating raw water of the above composition andhaving a DH 0! 9.93, a solution of di-sodium phosphate Na2HPOLH20) hasbeen successfully employed. The normal quantity of water including theith necessary steam to heat it to 230 F. for this case and which is tobe treated for the removal of all scale-forming salts is 850,000 poundsper hour. In proportion this amount equals about 85% city water asrepresented by the above analysis and 15% condensed steam. A chemicalmixing tank having a capacity of 30,000 pound of water is used todissolve the various chemicals used for treatment and keeps them in anagitated solution to be fed to the proportioner as indicated by thedemand. Each 30,000 pounds ofv water in the mixing tank has dissolved init 1% pounds of ferric sulphate, 64.0 pounds of dl- SOdilllIl phosphate,4.5 pounds of caustic soda. The resultant solution is proportionedmechanically to the water softener so that for each 100,000 pounds ofwater treated, 2.759 pounds of di-sodium phosphate, 0.282 pound ofcaustic soda, and 0.028 pound of ferric sulphate are added. The weightsof chemicals specified to be added produce a solution having a pHvalueof approximately 11.2. The pH value of this solution is maintainedregardless of the quantities of chemicals required for treatment of theboiler water.

With the chemical feed as indicated, the reaction acts to remove calciumand magnesium to quantities below their stoichiometric quantitiesaccomplished by chemical reaction and by ad sorption, all occurring in asolution of controlled pH value. which shall not be less than 7.8 andwhich is 8.3 in the case illustrated. All of the calcium and magnesiumas indicated is now in an insoluble state of which up to 99% hasprecipitated in the reaction chamber. The treated water then passes toanthracite filters where all of the remaining suspended solids areremoved thus producing crystal clear water having zero hardness and a pHvalue of 8.3.

While various filter constructions may be employed to mechanicallyremove the suspended solids in the treated water to provide a clearofhnent, I preferably utilize filters .fllled with anthracite which isnot aflfected by the phosphate solution, since standard filtersemploying calcite are not well adapted for this use, due to the factthat phosphate readily acts on the calcite material. Provision is alsomade in the filter conotruction for back washingin order to clean theter bed of the solids which plug the pore spaces.

It will, therefore, be apparent that an essential feature of thisinvention resides in providing completely treated boiler feed water ofrelatively low pH value, in which form cleaner steam is generated, andin which there are relatively less solids carried by the steam.

By carrying out the above procedure, it is found that water treated inaccordance with the present invention is satisfactory for all boilerpressures tilt tit

encountered in present power plant operation. him, the application ofthis method of treatment is 'ticularly desirable where added economy of"high pressures are desired and when, due to the nature oi the worlr,raw water must be used tor holler teed. lit also is an advantage, as ina case where ,tet condensers are installed and where by necessity it isnecessary to use raw water tor holler teed purposes. Under theseconditions it is: imperative that the boilers, in order to operate athluh capacities and at the same time produce clean steam, he tree oiscale and oludue.

Having thus described one illustrative emhodi" rn-cnt oi my inventionand the best mode known to me tor carrying out my method, I desire it tohe understood that clthouph specific terms are employed. they are usedin a generic and descriptive sense, and not for the purpose oflimitation, the scope of the invention being defined and limited only bythe terms of the appended claims.

I claim:

1. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the water a phosphate material of the group consisting of theortho-phosphates of the alkali metals to supply a phosphate radical inan amount sufficient to combine with all of the alkaline-earth metalpresent in the water upon complete reaction of the phosphate, and addingan iron compound which will produce iron ions in an amount not in excessof live parts per million by weight of the treated water but suflicientto act as a catalyst and cause complete reaction of the phosphate withthe alkaline-earth metal and form a phosphate complex ortho-phosphateprecipitate therewith.

2. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the water a phosphate material of the group consisting of theortho-phosphates of the alkali metals to supply a phosphate radical inan amount suflicient to combine with all of the alkaline-earth metalpresent in the water upon complete reaction. of the phosphate, andadding a compound selected from a group conslsting of the chlorides andsulphates of the iron to produce iron ions in arr-amount not in excessof five parts per million by weight of the treated water but suflicientto act as a catalyst and cause complete reaction of the phosphate withthe alkaline-earth metals to form a phosphate com.- plex precipitatetherewith.

3. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the water a phosphate material of the group consisting oi theortho-phosphates of the alkali metals to supply a phosphate radical inan amount sufllcient to combine with all of the alkaline-earth metalpresent in the water upon complete reaction of the phosphate, and addinga compound selected from a group of ferric salts consisting of thechlorides and sulphates of the iron to produce iron ions in an amountnot in excess of five parts per million by weight of the treated waterbut suilicient to act as a catalyst and cause complete reaction of thephosphate with the alkaline-earth metals to form a phosphate complexprecipitate therewith.

4. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the water a phosphate material of the group consisting of theortho-phosphates of the alkali metals to supply a phosphate radical inan amount sumcient to combine with all of the alkaline-earth metalpresent in the water upon complete reactionot the phosphate, and addingan iron compound which will produce iron ions in an amount betweenone-half of one part and rive parts per lllion by" weight oi the treatedwater to act as a catalyst and cause complete reaction oi the phosphatewith the alkaline-earth metal and term a phosphate complex: precipitatetherewith.

ll. "the process of softening water containing an slimline-earth metalcompound to produce colt waiter tor use in steam holders, whichcomprises uddinp to the rawwater on ortho-phosphate of the alkali metalsto cause to be present a phosphate radical in an amount suflicient tocombine with all of the alkaline-earth metals present in the water uponcomplete reaction of the phosphate, and adding an iron compound whichwill produce iron ions in an amount substantiaily two parts per millionby weight which functioning as a catalyst causes complete re-.

action of the phosphate and the alkaline-earth metals to form aphosphate complex precipitate therewith.

6. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the water a phosphate material of the group consisting of theortho-phosphates of the alkali metals to supply a phosphate radical inan amount sufiicient to combine with all of the alkaline-earth metalpresent in the water upon complete reaction of the phosphate, and addinga hydroxide and an iron compound which will produce iron ions in thepresence of a hydroxide in an amount not in excess of five parts permillion by weight of the treated water but 'suificient to act as acatalyst and cause complete reaction of the phosphate with thealkaline-earth metal and form a phosphate complex ortho-phosphateprecipitate therewith.

7. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the water a phosphate material of the group consisting of theortho-phosphates of the alkali metals to supply a phosphate radical inan amount suilicient to combine with all of the alkaline-earth metalpresent in the water upon complete reaction of the' phosphate, andadding a compound selected from a group consisting of the chlorides,sulphates, and hydroxides of iron to produce iron ions in an amount notin excess of five parts per million by weight of the treated water butsufficient to act as a catalyst and cause complete reaction of thephosphate with the alkaline-earth metals to form a phosphate complexprecipitate therewith.

8. The process of softening water containing an alkaline-earth metalcompound to produce soft water for use in steam boilers, which comprisesadding to the raw water an ortho-phosphate of the alkali metals to causeto be present a phosphate radical in an amount suflicient to combinewith all of the alkaline-earth metals present in the water upon completereaction of the phosphate, and adding an iron and hydroxide compoundwhich will produce iron ions in an amount substantially two parts permillion by weight which functioning as a catalyst causes completereaction of the phosphate and the alkaline earth metals to form a.phosphate complex precipitate therewith.

9. The process of softening raw water containing an alkaline-earth metalcompound to,

,produce when dissolved a pH value of substantially 8.3, adding to thewater the selected phosphate having such characteristics and in anamount sufiicient to combine with all of the functioning as a catalystto cause the phosphate to react to completion and combine with all ofthe alkaline-earth metal whereby substantially the complete removal ofthe alkaline-earth metal from the water undergoing treatment will besecured and after settling, soft water of substantially zero hardnesshaving a pH value of substantially 8.3 will be obtained.

10. The process of preventing the formation of adherent scale in steamboilers by steam boiler water, which comprises maintaining a continuousfeed of raw water containing an alkaline-earth metal compound intowater-softening equipment in the feed line to steam boilers, treatingthe raw water passing through said water-softening equipment by, makingadditions to the water therein of a phosphate material which is anamount suflicient to combine with all of the alkaline-earth metalpresent in the water if reaction of the phosphate therewith is allowedto go to completion, causing the phosphate to react with thealkaline-earth metal in the presence of iron ions in an amountsufficient to act as a catalyst to cause the phosphate to react tocompletion and combine with all of the alkalineearth metal and form aphosphate complex precipitate therewith whereby substantialy thecomplete removal of the alkaline-earth metal from the raw water beingtreated is secured and soft clear water of zero hardness is obtainedafter settling and removal of the precipitated material, and maintaininga continuous feed through the feed line to the steam boilers of theeilluent of soft clear zero-hardness water thus formed in thewater-softening equipment.

11. The process of softening raw water containing an alkaline-earthmetal compound to produce soft water for use in steam boilers, whichcomprises maintaining a continuous flow of raw feed water, initiallydetermining the pH of the raw water, and then on the basis of such pHdeterminations selecting a phosphate material of a type which if presentin solution in-the raw water in an amount sufiicient to react tocompletion and combine with all of the alkaline-earth metal will give apH- of 8.3 and will produce after settling of the precipitated materialssoft clear water of zero hardness, adding to the raw water prior to itsintroduction into the boiler an iron compound and a phosphate materialof such selected type and in a quantity sufficient to react tocompletion with all of the alkaline-earth metal, said phosphate materialbeing selected from the group of ortho-phosphates of the alkalimetals,and said iron compound being selected from the group of ferric saltsconsisting of ferric chloride and ferric sulphate, allowing the'reac-vtion of the phosphate with the alkaline-earth metal to proceed tocompletion in the presence of the iron compound which will serve tosupply ferric ions into the water in an amount suflicient to act as acatalyst and not in excess of five parts per million of the treatedwater to cause the phosphate to go to completion and combine with thealkaline-earth metal and form a phosphate complex precipitate therewithwhereby substantially the complete removal of the alkaline-earth metalfrom the water undergoing treatment is secured and a soft clear water atzero hardness having a pH value of 8.3 will be obtained after removal ofthe precipitated material, thereafter checking from time to time thephosphate radical concentration and hardness of the softened water thustreated, and on the basis of such determinations making additions asrequired of additional quantities of the phosphate material and the ironcompound in the same relative ratio as when used in the initialsoftening treatment of the raw water and in amounts sufficient tomaintain in the final soft Water when fed to the boiler an excessphosphate concentration for complete reaction and an iron ionconcentration of not in excess of five parts per million but sufflcientto act as a catalyst.

12; The process of softening raw water containing an alkaline-earthmetal compound to produce soft water for use in steam boilers, whichcomprises initially determining the pH of the raw water, and then on thebasis of such pH determinations selecting the type of phosphate materialfrom the alkali metal phosphates to be used which, if present in the rawwater in an amount sufiicient to completely react and combine with allof the alkaline-earth metal to produce final soft water of zerohardness, will also produce when dissolved at desired pH value add-' ingto the water the selected phosphate having such characteristics and inan amount sufficient to combine with all of the alkaline-earth metal inthe raw water upon the complete reaction of the phosphate, and adding acompound selected from a group consisting of the hydroxides, chloridesor sulphates of iron and in an amount to produce iron ions not in excessof five parts per million of the treated water for functioning as acatalyst to cause the phosphate to react to completion and combine withall of the alkalineearth metal whereby substantially the completeremoval of the alkaline-earth metal from the water undergoing treatmentwillbe secured and after settling, soft water of.substantially zerohardness having a desired pH value will be obtained.

13. The process of softening raw water containing an alkaline-earthmetal compound to produce soft water for use in steam boilers, whichcomprises maintaining a continuous flow of raw feed. water, initiallydetermining the pH of the raw water, and then on the basis of such pHdeterminations selecting a phosphate material of a type which if presentin solution in the raw water in an amount suflicient to react tocompletion and combine with all of the alkalineearth metal will give adesired pH and will produce after settling of the precipitated materialssoft clear water of zero hardness, adding to the raw water prior to itsintroduction into the boiler a hydroxide compound containing .iron and aphosphate material of such selected type and in a quantity sufficient toreact to completion with all of the alkaline-earth metal, said phosphatematerial being selected from the group of orthophosphates of thealkali-metals, and said iron in the hydroxide compound being obtainedfrom the group of ferric salts consisting of ferric chloride and ferricsulphate and ferric hydroxide, a1- lowing the reaction of the phosphatewith the alkaline-earth metal to proceed to completion in the presenceof the iron compound which will serve to supply ferric ions into thewater in an amount sufficient to act as a catalyst and not in excess offive parts per million of the treated water to cause the phosphate to goto completion and combine with the alkaline-earth metal and form aphosphate complex precipitate therewith whereby substantially thecomplete removal of the alkallne-earth metal from the water undergoingtreatment is secured and a soft clear water of zero hardness having adesired pH value will be obtained after removal of the precipitatedmaterial, thereafter checking from time to time the phosphate radicalconcentration and hardness of the softened water thus treated, and onthe basis of such determinations making additions as required ofadditional quantities of the phosphate material and the iron compound inthe same relative ratio as when used in the initial softening treatmentof the raw water and in amounts sufficient to maintain in the final softwater when fed to the boiler an excess phosphate concentration forcomplete reaction and an iron ion concentration of not in excess of fiveparts per million but suflicient to act as a catalyst.

ERNEST F. WALSH.

